With the common use of polymeric or plastic pipe in many fluid handling systems, such as systems for domestic gas and water distribution, tapping tees for plastic pipe, which are also constructed of plastic, have come into widespread use. A tapping tee assembly generally incorporates a metal rotating cutter contained in a mounting collar portion of the tapping tee for allowing the tee to be positioned at any desired spot along a main plastic pipe to be tapped. The tapping tee has a saddle portion which conforms to the diameter of the pipe to be tapped, a through-bore path for the cutter, and also has an integral side outlet adapted for mounting to a branch connection.
The tapping tee is first attached securely to the main plastic pipe to be tapped by any suitable means. For example, the tee can be attached by fusing the saddle portion of the plastic tee assembly to the main plastic pipe with the use of a heating iron or the like. Thereafterwards, the metal cutter is rotatably advanced through the sidewall of the main plastic pipe to cut an opening therethrough, and the cutter is then withdrawn from the main pipe for establishing an open fluid passage between the main plastic pipe and the side outlet in the tee assembly. Movement of the cutter within the tee assembly is accomplished by using drive threads which are provided externally on a section of the cutter, and internally within the through-bore of the tapping tee.
Heating irons for attaching the plastic saddle of the tapping tee to the main plastic pipe have found widespread use. The heating iron typically has a curvature complementary to the curvature of the tapping tee saddle to facilitate simultaneous heating of the surfaces of the saddle and the plastic pipe until the plastic at the junction of the two surfaces softens. When sufficient softening has occurred, the heating iron is removed and the saddle of the tee is directly fused to the main pipe.
Many designs for tapping tee cutters for plastic pipe, which are capable of retaining a cut coupon within the cutter after completion of the tapping operation, have been proposed but the majority of these cutters rely on compression of the coupon within a hollow coupon receiving portion of the cutter. While such coupon compression designs have been successfully utilized in many tapping tees, such designs can encounter difficulties due to temperature expansion and contraction of the plastic pipe being tapped. This is because the amount of compression required to retain the cut coupon varies with the actual temperature in the plastic pipe being tapped.
I have discovered that the addition of internal threads in the hollow coupon receiving portion of the cutter, preferably of the same design and pitch as the external drive threads of the cutter, eliminates the need for compressed retention of the coupon. Instead, the coupon is retained by the internal threads of the cutter, and the threaded retention of the coupon is effective over a wide temperature range.
It is therefore an object of this invention to provide improved method and apparatus for tapping a plastic pipe.
Another objective of this invention is to provide method and apparatus for tapping a plastic pipe wherein a cut coupon is retained in an internally threaded hollow portion of the tapping tee cutter upon completion of the tapping operation.